Interpretive Summary: Ich is a well-known parasite to fish; anyone who has tried to raise fish in an aquarium is familiar with it. Potassium permanganate (KMnO4) has been used to treat fish with Ich in the past, but scientific research has not proven its effectiveness. In this study we determined the amount of KMnO4 that will kill young Ich, and the concentration needed to prevent adult Ich from growing on small channel catfish and blue tilapia. We found that 0.9 ppm KMnO4 killed more than 95% of the young Ich in 4 hrs. In an experiment with catfish, small fish were exposed to young Ich and immediately treated with different amounts of KMnO4. A concentration of 1.0 ppm KMnO4 was found to stop the life-cycle. In another experiment, small blue tilapia were exposed and treated as above. A concentration of 0.5 ppm KMnO4 was found to stop the life-cycle. An additional experiment (without KMnO4) showed that small channel catfish were 33 times more likely to get Ich than small blue tilapia. Results show that KMnO4 will kill young Ich at low doses. But, good treatment of the fish will depend on the amount of other things KMnO4 can react with in a pond (like plants and fish food), and water temperatures which control the life-cycle of Ich. This research is a part of the U.S. Food and Drug Administration's requirement to get a new drug approved for use in aquaculture. 1

Technical Abstract:
Potassium permanganate (KMnO4) has been used to control infestations of Ichthyophthirius multifiliis, but reports of its effectiveness have not come from controlled efficacy studies. The purpose of this study was to determine the acute toxicity of KMnO4 to the I. multifiliis theront and the concentration needed to prevent an initial infestation of I. multifiliis in juvenile channel catfish (Ictalurus punctatus) and blue tilapia (Tilapia aurea). Ichthyophthirius multifiliis theronts were exposed to concentrations of KMnO4 in 100 ?l of well water in 96-well plates and observed for 4 hrs to determine the acute toxicity. A concentration of 0.9 mg KMnO4/L caused > 95% mortality of the theronts in 4 hrs in well water; the 4 hr LC50 value was estimated to be 0.77 mg/L. Juvenile channel catfish were exposed to 10,000 theronts/L of well water and immediately treated with a single dose of KMnO4. Infestation occurred in controls 6 days after exposure. The lowest effective dose of KMnO4 was 1.0 mg/L. Juvenile blue tilapia were exposed and treated as the catfish above. Infestation occurred in controls by day 8 after exposure. The lowest effective dose of KMnO4 was 0.5 mg/L. An additional experiment (without KMnO4) indicated that channel catfish were 33-fold more susceptible to I. multifiliis infestation than blue tilapia. These results indicate that KMnO4 is toxic to I. multifiliis theronts at low concentrations in clean water. However, effective treatment of pond water will be strongly influenced by detoxication of KMnO4 based on the concentration of easily oxidizable substances in the water.